There are many types of processors used to granulate, create spherical particles, and coat powders, seeds, pharmaceuticals, beads and other types of particulate material. For example, granulating methods include tumbling, agitating, extruding, disintigration, and fluidized beds. Some apparatus rotate the container, while other apparatus rotate a disk or rotor within a fixed container.
A rotor processor, also known as a centrifugal tumbling processor, has a narrow annular slit between the inner wall of the cylindrical container or chamber, and an outer peripheral edge of the rotatable rotor. The width of the slit is narrow so as to prevent particles in the chamber from falling through the slit. Air is forced upwardly through the slit as the rotor rotates within the chamber. The rotor forms a floor in the chamber upon which the powder or particles is supported. Rotation of the rotor and parts applies centrifugal force to the particles, which are thrown to the wall of the stator. Particles in the chamber are tumbled by the centrifugal force of the rotating rotor and the lifting force of the air passing upwardly through the slit.
The width of the slit governs the air velocity at the slit for a given air flow, which creates an upward draft that carries the particles upwardly. The upward movement of the particles continues, so long as the air velocity exceeds the transport velocity required to fluidize the particles. The air passes through the small gap with a relatively high velocity, and then expands into the larger volume of the stator chamber, thereby loosing velocity. As the particles loose their transport velocity, they fall back toward the center of the rotor and return to the rotor surface. The air slit velocity must exceed the transport velocity of the particles at all times, to prevent particles from passing downwardly through the slit.
Certain rotor processes require that a high slit velocity be achieved with a low volume of air flow, which necessitates that the slit be very narrow. Other processes, such as drying, require a large volume of air flow, which results in a large pressure drop across the slit. If the pressure drop is too large, then the static capacity of the air source, such as a blower, may be exceeded and the desired air flow is not achievable. In order to reduce the static pressure drop at larger air flows, it is necessary to increase the slit width or improve the inlet and exit geometry of the slit. In the prior art, the slit dimension has been modified using mechanical devices, such as levers or screws to raise and lower the rotor. In such prior art, movement of the rotor requires two steps: first, increasing the air flow potential, and second, adjusting the rotor slit, so as not to lose transport velocity of the particles in the chamber.
Therefore, a primary objective of the present invention is the provision of an improved rotor processor.
Another objective of the present invention is the provision of a rotor processor having a floating rotor for adjusting the slit dimensions.
A further objective of the present invention is the provision of a rotor processor wherein the slit dimension is automatically adjusted without human intervention.
Still another objective of the present invention is the provision of a rotor processor wherein the air pressure drop across the slit is maintained substantially constant as the slit dimension varies.
Yet another objective of the present invention is the provision of a rotor processor wherein the rotor is slidably mounted upon a rotor drive shaft for upward and downward movement along the shaft.
Another objective of the present invention is the provision of a rotor processor wherein the rotor is raised and lowered by air pressure.
Yet another objective of the present invention is the provision of an improved rotor processor having the ability to adjust the point at which a rotor lifting force exceeds a rotor resisting force.
Still another objective of the present invention is a method of processing particulate material in a rotor processor wherein the rotor is automatically raised and lowered in response to lifting and resisting forces.
Another objective of the present invention is the provision of an improved rotor processor which is efficient and effective in use.
These and other objectives will become apparent from the following description of the drawings and specification.